The invention relates to a recording and/or reproducing apparatus for a magnetic tape, which apparatus comprises at least one rotatable magnetic head which scans the magnetic tape along information tracks and which is mounted on a support which comprises a hub, by means of which the support is mounted on a rotatable shaft. Such apparatus, whether for recording or playback, will hereafter be called a rotary scanning tape recorder.
The support for such a tape recording includes at least one hollow cylindrical portion, which is coaxial with the shaft, which projects axially from the hub and which cooperates with a releasable clamping device for clamping the portion onto the shaft. The clamping device comprises an axially adjustable clamping ring which is coaxial with the shaft. The clamping ring has three clamping projections which project radially towards the shaft to act on the cylindrical portion, which are inclined equally relative to said shaft, which are arranged axially symmetrically relative to the shaft; that is, the projections are arranged about the shaft axis as an axis of symmetry such that the angular distances of the projections from each other are equal. For adjusting the clamping ring, the device also includes a rotatable adjusting ring which cooperates with the clamping ring and which is coaxial with the shaft, the clamping projections clamping the cylindrical portion onto the shaft by means of the clamping ring upon rotation of the adjusting ring.
Such a tape recorder is disclosed in Austrian Pat. No. 365,808, to which U.S. Pat. No. 4,464,690 corresponds. For adjusting, this recorder has an adjusting ring which engages the support through a screwthread, the movement of the adjusting ring being transmitted to the clamping ring via a thrust ring. In order to clamp the cylindrical portion of the hub of the support onto the shaft the support must be retained and the adjusting ring must be tightened. As a result of the large frictional forces acting between the threaded surfaces, between the adjusting ring and the thrust ring, and between the thrust ring and the clamping ring, during clamping the support must be retained with comparatively large forces when it is mounted. However, these forces give rise to internal stresses in and deformations of the support, which persist at least for the greater part after clamping has been completed and give rise to both a radial and an axial eccentricity during rotation of the support. An eccentric non-uniform rotation of the support adversely affects the scanning of the information tracks by the magnetic head during the recording and/or reproduction of information. Moreover, the clamping ring of the clamping device of the known apparatus may also rotate when the adjusting ring is tightened during clamping, so that the clamping projections of the clamping ring rub over the cylindrical portion of the support. This gives rise to a groove-like irregular deformation of the cylindrical portion which is undesirable because the three clamping projections should exert large and equal clamping forces which are reproducible after the clamping device has been released and retightened.